Dispenser oath are also called matrix cathodes or reserve cathodes. They consist, in general, of a dispenser body, also called a metal matrix, which is pressed or sintered from a metal powder and is impregnated with the actual emission material. Metals such as tangsten and molybdenum can be considered for use as the metal powder for the dispenser body. The use of mixtures of such metal powders has been known as well. Pressing the dispenser body into a cavity of a cathode sleeve has been known from German Offenlegungsschrift No. DE-OS 20,48,224. For example, building up the dispenser body in layers has been known from German Offenlegungsschrift No. DE-OS 41,14,856. The porous matrix body can be impregnated with an emission material, which consists of, e.g., BaO-CaO-Al.sub.2 O.sub.3, by impregnation, melting in or the like.
It was found, in general, that so-called mixed-metal matrix cathodes (MM cathodes), i.e., cathodes whose dispenser bodies are pressed and sintered from a metal powder mixture, have improved dimensional stability and better current stability. The dispenser bodies of mixed-metal matrix cathodes consist, in general, of metals of a first group, such as tungsten, chromium or molybdenum, and metals of a second group, such as iron (Fe), cobalt (Co), nickel (Ni), ruthenium (Ru), rhodium (Rh), palladium (Pal), rhenium (Re), osmium (Os), iridium (It), and platinum (Pt).
Adding tungsten or tungsten oxide to the emission material has also been known from German Patent No. DE-PS 30,17,429.
It has also been known that the emission capacity of the cathodes can be improved by adding scandium compounds to the cathode body or to the emission material. However, the long-term properties of these so-called "Scandat cathodes" are not yet satisfactory.